Thursday, December 27, 2007

Basic Fielding Stats - 2007

Today's article is the first in a series of articles looking at individual fielding statistics for the Tigers and the rest of baseball in 2007.It is more difficult to measure fielding than hitting or even pitching so I will discuss several different options over the next couple of weeks.I will start with the most basic of fielding stats and work my way up to the more sophisticated modern methods.Finally, I will rank the players at each position by aggregating all the stats.Today I’ll give a brief history of fielding stats and a discuss the most frequently used measures.After that, I’ll show how the Tigers rank on these measures.In future posts, I’ll discuss some of the newer fielding measures. The Table of contents for the series is listed below:

The most commonly reported fielding measure is fielding percentage (FPCT) which is the infrequency with which fielders make errors on balls which they reach. It is calculated as (Total plays – errors)/total plays. Not making errors is a positive thing so this statistic has some value but it also has some important flaws. First, errors are subjective and judgement varies from one official scorer to the next.

More importantly, FPCT says nothing about range. Some players get to a lot of balls which other players can not reach. Measurement of range is an area of sabermetrics which is still developing. The two most accessible range statistics, Range Factor (RF) and Zone Rating (ZR), are discussed below.

Range Factor (RF) was originated by baseball writer Al Wright in the 1870s but it was virtually ignored for over 100 years until Bill James re-introduced it around 1980. Range Factor = (put outs + assists)/games. One of the limitations of RF is that it is a team dependent statistic. For example, an outfielder playing behind a predominantly ground ball staff will have fewer opportunities than an outfielder on a staff with a lot of fly ball pitchers. Similarly, the range factors of all fielders on a team will be affected if their pitchers strike out a lot of batters.

Zone Rating (ZR) was developed by John Dewan when he worked at STATS, Inc in the early 1990s. They divided the baseball field into small areas and assigned these areas to fielders as follows: Based on hit location data, if half the balls hit into a certain area are converted into outs by all he players at a given position, then that area is considered to be part of the zone for that position. For example, if 1,000 balls are hit into area X and 506 are converted into outs by baseball's shortstops, then Area X is considered to be part of the zone for the shortstop position.

The calculation of ZR for a given player considers three factors: The number of balls hit into his zone while he is in the game (Balls In Zone or BIZ) , the number of these balls which he converts into outs (Plays in Zone or PIZ) and the number of plays he makes outside his zone (Outside of Zone or OOZ). The ZR is computed as follows:

ZR= (PIZ+OOZ)/(BIZ+OOZ).

So, ZR can be regarded as the percentage of balls in a player's zone that he converts into outs plus extra credit for successful plays he made outside his zone. Since Zone Rating penalizes a player for errors by considering them to be missed opportunities, it makes FPCT almost obsolete.

One of the problems with zone rating is that it depends on the reliability of those collecting the data. They need to judge whether balls were actually hit into the zone and distinguish between fly balls and line drives as there is a different zone for each. Another drawback of zone rating is that it treats all balls in the zone the same way even though it may be more difficult to reach some balls within the zone than others.

Table 1Shows how Tiger fielders (2007 Tigers and recent acquisitions) rank on FPCT, RF and ZR among players with 600 or more innings in 2007.Fielding percentage does not tell us much about fielding performance but has been included on the table to show how deceptive it can be in evaluation of fielding.The discrepancies between range factor and zone rating, two statistics which are supposed to measure the same thing tell us they are not completely reliable. Zone rating is considered to more reliable because it is not as team dependent. In fact, Range Factor is rarely used by sabermetricians anymore.

Using Curtis Granderson as an example, the table tells us the following: There were 27 MLB center fielders who played 600 or more innings in 2007. Granderson had a .989 FPCT which placed him 14th in baseball. His 3.04 RF means that he made about 3 plays per game. He ranked 2nd in baseball on that statistic. His ZR was .908 which says that he converted 90.8% of the balls in his zone into outs (including extra credit for plays he made outside his zone). He ranked 4th in the majors on that measure.

Among others who did well on Zone Rating was Sean Casey who finished 7th in the majors. Note that range measures may not tell us as much about first basemen as they do for other fielders because they do not address throws taken from infielders and this is obviously an important part of a first baseman's job.

Others who ranked well on ZR were third baseman Brandon Inge (4th in the majors), center fielder Jacque Jones (6th) and Magglio Ordonez (2nd). The biggest surprise in that group is probably Ordonez. He definitely seemed to improve last year but 2nd is better than I expected. ZR is just one range measure though. We will see how these players rank on other measures when we get to them.

Another interesting case is Placido Polanco who had a perfect FPCT but finished only 13th in ZR. That is an illustration of one of the problems with fielding percentage - it ignores how much ground a player covers. It also might surprise some people that Edgar Renteria ranked even lower (23rd) in ZR than Carlos Guillen (20th). Again, ZR is just one zone measure. I always recommend looking at more than one measure when evaluating fielding.

Note that these statistics don’t really pertain to catchers so that position will have to be addressed at another time.

The statistics for the table below were abstracted from the ESPN database.

2 comments:

I just added a link to the fielding data near the bottom of my post just above the table. He finished behind Sizemore, Wells and Crisp. I'm also going to look at some other range measures. Then I'm going to take the average of all the measures and see who the leaders are at each position.